(1) Field of the Invention
The present invention relates to injectors for administering a medication.
(2) Description of Related Art
Various types of injectors for administering a medication are known. In some cases, the injector is capable of holding medication sufficient for multiple doses. For each dose, the user selects the amount of medication to be injected, for example by dialing a dose set knob, and then injects that selected dose. This may be done for multiple doses over a period of time, until all of the medication in the injector has been dispensed.
Such injectors may be useful for various types of medication. For example, many diabetic patients self-inject insulin multiple times each day using an injector device or pen. Many such pens are operated by the patient dialing the required dose and then self-injecting the selected dosage amount. Because the patient is constantly using an injector pen on a daily basis, users will frequently require changing to a new injector when the insulin supply is exhausted. Sometimes, as the injector pen is approaching the end of its insulin supply, the injector does not contain enough insulin to provide the full dose for this last injection.
In many injectors, as the dose is being selected or dialed, the amount of the selection is indicated to the user, for example on a scale that is visible through a window of the injector housing. As the selected dose is being injected, the scale returns in accordance with the amount injected. Thus, when the full amount of the selected dose is injected, the scale returns from the selected amount back to the zero position. If less than the full amount of the selected dose is injected, the scale returns only by the amount that has been injected, such that after the partial injection the scale shows the difference between the amount selected and the amount injected.
Conventionally, there have been two ways of handling the situation when there is only a partial dose remaining in the injector pen. In the first way, the user sets the dose the same way as the prior doses, by dialing the dosage knob to the full amount of the desired dose. When only a partial dose of medication remains in the pen, this set dose exceeds the remaining amount of medication. The user may not be aware that the set dose exceeds the available medication. When the user injects the medication, the delivery mechanism will stop when the full available amount of medication has been delivered, because the piston rod inside the injector cannot advance any further. In this case, the scale of the injector pen indicates the portion of the selected dosage amount that was not dispensed, which the user must supplement with an additional injection from a new injector pen.
In the second way, an “active-stop” injector, the dosage knob prevents the user from dialing a dose that is greater than the amount of medication remaining in the pen. Thus, the injector itself will indicate to the user that only a partial dose remains, which indication will occur at the time the user attempts to set a dose higher than the amount of remaining medication.
In using both types of injector pens, the user should perceive that the old injector pen is near empty and have the new injector pen ready to inject the supplemental make-up dose. But if the user only becomes aware of the last remaining dose too late, such as only when the injector is empty or only upon attempting to dial a dose, the user may not have prepared the new injector pen for use. Because insulin pens are commonly stored in the refrigerator for preservation, an unaware user would have to retrieve a new injector from the refrigerator and administer a cold injection for the supplemental dose, which is uncomfortable. Otherwise, the user will have to wait until the new injector pen is warmed to room temperature, which can be inconvenient.
In addition, many “active-stop” injector pens have numerous parts. Certain “active-stop” injector pens can be relatively expensive to manufacture.